This invention relates to an epoxy resin, an adhesive composition containing such an epoxy resin, a process for producing such an epoxy resin having good flexibility and use of the adhesive composition for producing a semiconductor device.
As aromatic epoxy resins, there have been known bisphenol A type, bisphenol F type and bisphenol AD type epoxy resins obtained from bisphenol and epichlorohydrin, phenol novolak type epoxy resins and cresol novolak type epoxy resins obtained from novolak resins, and naphthalene skeleton-containing or alicyclic epoxy resins. These aromatic epoxy resins are used together with amine curing agents, acid anhydride curing agents, phenol resin curing agents, or the like, as casting resins, molding materials for electric and electronic parts, etc. With the development of recent technology, it is desired to have a lower modulus of elasticity.
On the other hand, as epoxy resins containing siloxane linkages, there have been known 1,3-bis(3-glycidoxypropyl)-1,1,3,3-tetramethyldisiloxane, 3-glycidoxypropyldimethylpolysiloxane, etc. But, it is impossible to lower the modulus of elasticity when 1,3-bis(3-glycidoxypropyl)-1,1,3,3-tetramethyldisiloxane is used. Further, when 3-glycidoxypropyldimethylpolysiloxane is used, the modulus of elasticity can be lowered, but heat resistance is also lowered.
Thus, an epoxy resin which can lower the modulus of elasticity without lowering heat resistance is desired.
On the other hand, in the assembly of resin encapsulated semiconductor devices, solder or electroconductive adhesives have been used in order to lower the production cost in a step of bonding IC's, LSI's, etc. to lead frames. As the electroconductive adhesives, there are generally used compositions comprising an epoxy resin mixed with a silver (Ag) powder, a novolak type phenol resin as a curing agent for the epoxy resin (bisphenol A type or novolak type) and a curing accelerator such as an imidazole as disclosed in Japanese Patent Examined Publication No. 63-4701.
Recently, with higher density of integration of LSI's, chips are enlarged. On the other hand, lead frames of iron alloys such as 42 alloy lead frames are to be substituted with copper frames. When chips are bonded to such copper frames using the above-mentioned epoxy resin adhesive, warpage of chips becomes larger with the enlargement of chips, resulting in changing properties. The warpage of chips is caused by stress generated from a difference in thermal expansion coefficients of chips and copper (chips 3.5.times.10.sup.-6 l/.degree.C, copper frame 17.times.10.sup.-6 l/.degree.C, 42 alloy lead frame 4.4.times.10.sup.-6 l/.degree.C).
The warpage of chips also depends on a modulus of elasticity of adhesive. The smaller the modulus of elasticity becomes, the smaller the warpage of chips becomes due to absorption of the stress mentioned above.
Therefore, adhesives having a low modulus of elasticity which can absorb the stress between chips which are to be enlarged more and more hereinafter and copper frames, and rapid curing properties are demanded.